Method of treating unvulcanized rubber surfaces



No Drawing.

Patented Aug. 4, 1 i931 1 wInLisAeIBn ons; OF GREAT, 'nEoK, NEW YORK, Assronon To MORGAN a WRIGHT, or v DETROIT, lMItfiflIGAN A COBIQBATIQN or MICHIGAN -men 'QQEa BEA TING iinvtI onnIzEn R BBER seam ess:

This invention relates to methods for preventing or controlling the surface stickiness of unvulcanizeclrubber stocks incident to their manufacture into articles. 1

In the manufacture of rubber; goods and articles, particularly those requiring assern:

bly fromcalendered or ,sheetedrubbenit has 1 been necessary to separate the sheets-or layersfof rubber with fabric, paper or: otherliner during transport or delays incident to manufacture. Ithas also been" the practice; to treat the layers of rubber with some material which prevents the adhesion of the unvulcanized sheets pr1orto thefabrioation ofthe '15 completed article. The use ofjliners of vary ous sorts has beenfor manypurposes more or less of an expense, as the; stock mustbe handled several times, and as the liners, or books must also be handled. l The, majority of the materials applied to the surface ,of the rubber as lubricants or. preventatives of ad-- hesion are of a mineral nature, these being dusted on or applied as suspensions or emul sions. Such materialsj -include' soapstonel,

starches, and other powdered substances hav-.

ing similar properties. The use of such min-v eral products is attended by certain disad-' vantages notable among which are the tendency to adhere to the surface of the rubber, likelihood of causing discoloration during I vulcanizatiom'and interference with the ad hesion of one layer of rubber to another when, such adhesion is desired. It has also been proposed to employ metallic salts having a lubricating or tack-reducing nature, and hav,--

ing some: property of being absorbed by the rubber at vulcanization temperature. However, these metallic salts may exert some influence upon the rate of vulcanization, particularly in the presence of powerful accelerators, and they frequently require a sol-- vent other than water inorder to apply them successfully as suspensions or 9 solutions, either with or without water. Obviously the use of a solvent even in small quantities is not always desirable. Further the metallic Q r salts are not freely soluble-in the rubber except at the higher vulcanization temperatures, whereas formany manufactur ng pur- 50v posesit is particularlydesirable to secure the Application file dOetOberH, 1927. Serial No. 226,260.

utmost adhesion between plies at tempera-' tures 1 considerably j below nthe v vulcanizin g The object of of unvulcanized' rubber surfaces 1 during the various manufacturingstages, but at the sametime possessing none of thedisadvans tages above" mentioned. The invention also aims to provide a method for reducing the tackiness of unvulcanized rubbersurfaces w th a material" whichw1ll not rema1n on g the surface. of the rubber" atgtemperatures below those ordinarily employed in hotul, canization, nor, change the character of the rubber surface in any respect after'vulcanh,

zation. :1

, With a particular embodimentzin :mind'but,

without-intention to place limitations upon,

the scope of 'theinvention beyond @Vhalhmfly V be required by the prior art, the -inventionbriefly" stated consists in treating unvulcanized rubber, surfaces witha material which iswdecomposable at a the vulcanization temperatures nto portions whichare volatile and rubber-{soluble respectively, The i'n--v vention includes the use of materials} which I are c'ompletely volatile, as well as materials: c which 7 are decomposed into; constituents eithergvolatileor soluble in-rthe rubber or both.

As an illustration of a tackiness-reducing} material which is decomposableat vl ilcaniz-. ingtemperature,

tousesuch substances aspthe' volatile salts of; organic acids, particularly those acids whlch contain 8.0r more carbonatoms', :Am-

' monium, stearate is one example. This mate-l rial may 'beused in the following" manner:; A- solution of QO/Jparts of ammonium stea-U afwhitish film is leftnpon-zthe thepresent invention is to I provide a method for reducing the-tackiness into-a volatile-'portionand a'portion readily soluble in rubber, I prefer:

plies or sheets. Upon heating, assuming that the calender-ed sheets are to be plied, the ammonium stearate layer is decomposed, with the evolution of gaseous ammonia and leaving free stearic acid on the surface of the rubber. The stearic acid, however, is readily soluble in rubber at comparatively low temperatures, for example at 100 (1., and quite rapidly soluble at higher tempera-, tures. If the treated rubber be warmed for a few minutes at 100 C. it will be observed that the surface ofthe rubber isrestored .to its original brightness, showing that none of the material has remained on the surface. With rubber stocks containing powerful accelerators which bring about vulcanization at low temperatures, the use of ammoni um stearate as a surface lubricant is highly satisfactory, for the reason that complete solution of the stearic acid ,'and evolution of the ammonium base can be accomplished without heating the rubber in excess of the low temperatures at which vulcanization is intended to be'accomplished.

Preferably the materials employed are completely soluble in water, although they may be colloidally soluble. Illustrations of other materials which are either completely volatile at vulcanization temperature or'are decomposed into portions volatile at the vulcanization temperature and/or soluble in the rubber, are the volatile base compounds of the fatty acids, palmitic acid, oleie, and similar materials. It will be observed that none of thesematerials leave in the rubber-or introduce into the rubber any substance which has a material effect upon the rate ofvulcanization. None of the substances employed in the present invention change the surface characteristics of the rubber after they have been removed. Their use eliminates the necessity of providing liners or books for the storage or transportation of unvulcanized rubber sheets, and does not cause any deposit or cak-ing'in molds. There is practically no change in the color of a rubber stool: which has been treated with the materials of the present invention, nor do they cause the finished surfaces to becomedulled or dusty looking.

Having thus I claim and desire to ent is: y p

1. Method of reducing the tackiness of unvulcanized rubber surfaces which comprises treating the rubber surface with a tackiness-reducing compound which is decomposable at vulcanizing temperatures into portions at least one of which is volatile said tackiness reducing compound being capable of leaving substantially no deposit on the surface of the rubber at the termination of vulcanization.

described my invention, what protect by Letters Pat- 2. Method of reducing the tackiness of un vulcanized rubber surfaces which comprises treating the rubber surface with a tackinessreducing material which is decomposable at vulcanizing temperatures into a volatile portion and a remaining rubber soluble portion said tackiness reducing material being capable of leaving substantially no deposit on the surface of the rubber at the termination of vulcanization.

'3. Method of ,redueingthe tackinessof unvulcanized rubber-surfaces which comprises treating the rubber surface with a solution of tackiness-reducing.material containing a portion volatile at vulcanizing temperatures and a remaining portion soluble in the rubberat said temperatures said tackiness reducing material being capable of leaving substantially no deposit on-the surf-ace of the rubber at the termination of vulcanization.

4:. Method of reducing the tackiness of unvulcanized rubber surfaces which com prisestreating the rubber surface with a solution of a higher fatty acid salt of a base volatile at vulcanizing temperatures.

5. Method of reducing thetackiness of unvulcanized rubber surfaces which comprises treating the rubber surface with an ammonium salt of a higher fatty acid soluble in the rubber at vulcan1zing temperature.

6. Method of reducing the tackiness ofunvulcanized rubber surfaces which comprises coating the rubber surface with a water solution of an ammonium salt of a higher fatty acid.

' 7 Method of reducing the tackiness of unvulcanized rubber surfaces which comprises coating the rubber surface with a water solution of ammonium stearate.

Signed at New York, New York, this 41th, day of October, 1927 WILLIS A. GIBBONS. 

